docs: def add(self, element):
          """
          Adds an element to the HyperLogLog. Datatype cardinality will
          be updated when the object is saved.
  
          :param element: the element to add
          :type element: str
          """
          if not isinstance(element, six.string_types):
              raise TypeError("Hll elements can only be strings")
          self._adds.add(element)